/*
 * Copyright 2002-2019 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.web.reactive.function.server;

import java.net.URI;
import java.time.Instant;
import java.time.ZonedDateTime;
import java.util.Arrays;
import java.util.Collections;
import java.util.EnumSet;
import java.util.HashMap;
import java.util.LinkedHashSet;
import java.util.List;
import java.util.Map;
import java.util.Optional;
import java.util.Set;
import java.util.function.BiFunction;
import java.util.function.Consumer;

import org.reactivestreams.Publisher;
import reactor.core.publisher.Mono;

import org.springframework.core.ParameterizedTypeReference;
import org.springframework.core.codec.Hints;
import org.springframework.http.CacheControl;
import org.springframework.http.HttpHeaders;
import org.springframework.http.HttpMethod;
import org.springframework.http.HttpStatus;
import org.springframework.http.MediaType;
import org.springframework.http.ResponseCookie;
import org.springframework.http.codec.HttpMessageWriter;
import org.springframework.http.server.reactive.AbstractServerHttpResponse;
import org.springframework.http.server.reactive.ServerHttpRequest;
import org.springframework.http.server.reactive.ServerHttpResponse;
import org.springframework.util.Assert;
import org.springframework.util.CollectionUtils;
import org.springframework.util.LinkedMultiValueMap;
import org.springframework.util.MultiValueMap;
import org.springframework.web.reactive.function.BodyInserter;
import org.springframework.web.reactive.function.BodyInserters;
import org.springframework.web.server.ServerWebExchange;

/**
 * Default {@link ServerResponse.BodyBuilder} implementation.
 *
 * @author Arjen Poutsma
 * @author Juergen Hoeller
 * @since 5.0
 */
class DefaultServerResponseBuilder implements ServerResponse.BodyBuilder {

    private final int statusCode;

    private final HttpHeaders headers = new HttpHeaders();

    private final MultiValueMap<String, ResponseCookie> cookies = new LinkedMultiValueMap<>();

    private final Map<String, Object> hints = new HashMap<>();


    public DefaultServerResponseBuilder(ServerResponse other) {
        Assert.notNull(other, "ServerResponse must not be null");
        this.headers.addAll(other.headers());
        this.cookies.addAll(other.cookies());
        if (other instanceof AbstractServerResponse) {
            AbstractServerResponse abstractOther = (AbstractServerResponse) other;
            this.statusCode = abstractOther.statusCode;
            this.hints.putAll(abstractOther.hints);
        }
        else {
            this.statusCode = other.statusCode().value();
        }
    }

    public DefaultServerResponseBuilder(HttpStatus status) {
        Assert.notNull(status, "HttpStatus must not be null");
        this.statusCode = status.value();
    }

    public DefaultServerResponseBuilder(int statusCode) {
        this.statusCode = statusCode;
    }


    @Override
    public ServerResponse.BodyBuilder header(String headerName, String... headerValues) {
        for (String headerValue : headerValues) {
            this.headers.add(headerName, headerValue);
        }
        return this;
    }

    @Override
    public ServerResponse.BodyBuilder headers(Consumer<HttpHeaders> headersConsumer) {
        headersConsumer.accept(this.headers);
        return this;
    }

    @Override
    public ServerResponse.BodyBuilder cookie(ResponseCookie cookie) {
        Assert.notNull(cookie, "ResponseCookie must not be null");
        this.cookies.add(cookie.getName(), cookie);
        return this;
    }

    @Override
    public ServerResponse.BodyBuilder cookies(Consumer<MultiValueMap<String, ResponseCookie>> cookiesConsumer) {
        cookiesConsumer.accept(this.cookies);
        return this;
    }

    @Override
    public ServerResponse.BodyBuilder allow(HttpMethod... allowedMethods) {
        this.headers.setAllow(new LinkedHashSet<>(Arrays.asList(allowedMethods)));
        return this;
    }

    @Override
    public ServerResponse.BodyBuilder allow(Set<HttpMethod> allowedMethods) {
        this.headers.setAllow(allowedMethods);
        return this;
    }

    @Override
    public ServerResponse.BodyBuilder contentLength(long contentLength) {
        this.headers.setContentLength(contentLength);
        return this;
    }

    @Override
    public ServerResponse.BodyBuilder contentType(MediaType contentType) {
        this.headers.setContentType(contentType);
        return this;
    }

    @Override
    public ServerResponse.BodyBuilder eTag(String etag) {
        if (!etag.startsWith("\"") && !etag.startsWith("W/\"")) {
            etag = "\"" + etag;
        }
        if (!etag.endsWith("\"")) {
            etag = etag + "\"";
        }
        this.headers.setETag(etag);
        return this;
    }

    @Override
    public ServerResponse.BodyBuilder hint(String key, Object value) {
        this.hints.put(key, value);
        return this;
    }

    @Override
    public ServerResponse.BodyBuilder hints(Consumer<Map<String, Object>> hintsConsumer) {
        hintsConsumer.accept(this.hints);
        return this;
    }

    @Override
    public ServerResponse.BodyBuilder lastModified(ZonedDateTime lastModified) {
        this.headers.setLastModified(lastModified);
        return this;
    }

    @Override
    public ServerResponse.BodyBuilder lastModified(Instant lastModified) {
        this.headers.setLastModified(lastModified);
        return this;
    }

    @Override
    public ServerResponse.BodyBuilder location(URI location) {
        this.headers.setLocation(location);
        return this;
    }

    @Override
    public ServerResponse.BodyBuilder cacheControl(CacheControl cacheControl) {
        this.headers.setCacheControl(cacheControl);
        return this;
    }

    @Override
    public ServerResponse.BodyBuilder varyBy(String... requestHeaders) {
        this.headers.setVary(Arrays.asList(requestHeaders));
        return this;
    }

    @Override
    public Mono<ServerResponse> build() {
        return build((exchange, handlerStrategies) -> exchange.getResponse().setComplete());
    }

    @Override
    public Mono<ServerResponse> build(Publisher<Void> voidPublisher) {
        Assert.notNull(voidPublisher, "Publisher must not be null");
        return build((exchange, handlerStrategies) ->
                Mono.from(voidPublisher).then(exchange.getResponse().setComplete()));
    }

    @Override
    public Mono<ServerResponse> build(
            BiFunction<ServerWebExchange, ServerResponse.Context, Mono<Void>> writeFunction) {

        return Mono.just(
                new WriterFunctionResponse(this.statusCode, this.headers, this.cookies, writeFunction));
    }

    @Override
    public <T, P extends Publisher<T>> Mono<ServerResponse> body(P publisher, Class<T> elementClass) {
        Assert.notNull(publisher, "Publisher must not be null");
        Assert.notNull(elementClass, "Element Class must not be null");

        return new DefaultEntityResponseBuilder<>(publisher,
                BodyInserters.fromPublisher(publisher, elementClass))
                .status(this.statusCode)
                .headers(this.headers)
                .cookies(cookies -> cookies.addAll(this.cookies))
                .hints(hints -> hints.putAll(this.hints))
                .build()
                .map(entityResponse -> entityResponse);
    }

    @Override
    public <T, P extends Publisher<T>> Mono<ServerResponse> body(P publisher,
                                                                 ParameterizedTypeReference<T> typeReference) {

        Assert.notNull(publisher, "Publisher must not be null");
        Assert.notNull(typeReference, "ParameterizedTypeReference must not be null");

        return new DefaultEntityResponseBuilder<>(publisher,
                BodyInserters.fromPublisher(publisher, typeReference))
                .status(this.statusCode)
                .headers(this.headers)
                .cookies(cookies -> cookies.addAll(this.cookies))
                .hints(hints -> hints.putAll(this.hints))
                .build()
                .map(entityResponse -> entityResponse);
    }

    @Override
    public Mono<ServerResponse> syncBody(Object body) {
        Assert.notNull(body, "Body must not be null");
        Assert.isTrue(!(body instanceof Publisher),
                "Please specify the element class by using body(Publisher, Class)");

        return new DefaultEntityResponseBuilder<>(body,
                BodyInserters.fromObject(body))
                .status(this.statusCode)
                .headers(this.headers)
                .cookies(cookies -> cookies.addAll(this.cookies))
                .hints(hints -> hints.putAll(this.hints))
                .build()
                .map(entityResponse -> entityResponse);
    }

    @Override
    public Mono<ServerResponse> body(BodyInserter<?, ? super ServerHttpResponse> inserter) {
        return Mono.just(
                new BodyInserterResponse<>(this.statusCode, this.headers, this.cookies, inserter, this.hints));
    }

    @Override
    public Mono<ServerResponse> render(String name, Object... modelAttributes) {
        return new DefaultRenderingResponseBuilder(name)
                .status(this.statusCode)
                .headers(this.headers)
                .cookies(cookies -> cookies.addAll(this.cookies))
                .modelAttributes(modelAttributes)
                .build()
                .map(renderingResponse -> renderingResponse);
    }

    @Override
    public Mono<ServerResponse> render(String name, Map<String, ?> model) {
        return new DefaultRenderingResponseBuilder(name)
                .status(this.statusCode)
                .headers(this.headers)
                .cookies(cookies -> cookies.addAll(this.cookies))
                .modelAttributes(model)
                .build()
                .map(renderingResponse -> renderingResponse);
    }


    /**
     * Abstract base class for {@link ServerResponse} implementations.
     */
    abstract static class AbstractServerResponse implements ServerResponse {

        private static final Set<HttpMethod> SAFE_METHODS = EnumSet.of(HttpMethod.GET, HttpMethod.HEAD);

        final int statusCode;
        final Map<String, Object> hints;
        private final HttpHeaders headers;
        private final MultiValueMap<String, ResponseCookie> cookies;


        protected AbstractServerResponse(
                int statusCode, HttpHeaders headers, MultiValueMap<String, ResponseCookie> cookies,
                Map<String, Object> hints) {

            this.statusCode = statusCode;
            this.headers = HttpHeaders.readOnlyHttpHeaders(headers);
            this.cookies = CollectionUtils.unmodifiableMultiValueMap(new LinkedMultiValueMap<>(cookies));
            this.hints = hints;
        }

        private static <K, V> void copy(MultiValueMap<K, V> src, MultiValueMap<K, V> dst) {
            if (!src.isEmpty()) {
                src.entrySet().stream()
                        .filter(entry -> !dst.containsKey(entry.getKey()))
                        .forEach(entry -> dst.put(entry.getKey(), entry.getValue()));
            }
        }

        @Override
        public final HttpStatus statusCode() {
            return HttpStatus.valueOf(this.statusCode);
        }

        @Override
        public final HttpHeaders headers() {
            return this.headers;
        }

        @Override
        public MultiValueMap<String, ResponseCookie> cookies() {
            return this.cookies;
        }

        @Override
        public final Mono<Void> writeTo(ServerWebExchange exchange, Context context) {
            writeStatusAndHeaders(exchange.getResponse());
            Instant lastModified = Instant.ofEpochMilli(headers().getLastModified());
            HttpMethod httpMethod = exchange.getRequest().getMethod();
            if (SAFE_METHODS.contains(httpMethod) && exchange.checkNotModified(headers().getETag(), lastModified)) {
                return exchange.getResponse().setComplete();
            }
            else {
                return writeToInternal(exchange, context);
            }
        }

        private void writeStatusAndHeaders(ServerHttpResponse response) {
            if (response instanceof AbstractServerHttpResponse) {
                ((AbstractServerHttpResponse) response).setStatusCodeValue(this.statusCode);
            }
            else {
                HttpStatus status = HttpStatus.resolve(this.statusCode);
                if (status == null) {
                    throw new IllegalStateException(
                            "Unresolvable HttpStatus for general ServerHttpResponse: " + this.statusCode);
                }
                response.setStatusCode(status);
            }
            copy(this.headers, response.getHeaders());
            copy(this.cookies, response.getCookies());
        }

        protected abstract Mono<Void> writeToInternal(ServerWebExchange exchange, Context context);
    }


    private static final class WriterFunctionResponse extends AbstractServerResponse {

        private final BiFunction<ServerWebExchange, Context, Mono<Void>> writeFunction;

        public WriterFunctionResponse(int statusCode, HttpHeaders headers,
                                      MultiValueMap<String, ResponseCookie> cookies,
                                      BiFunction<ServerWebExchange, Context, Mono<Void>> writeFunction) {

            super(statusCode, headers, cookies, Collections.emptyMap());
            Assert.notNull(writeFunction, "BiFunction must not be null");
            this.writeFunction = writeFunction;
        }

        @Override
        protected Mono<Void> writeToInternal(ServerWebExchange exchange, Context context) {
            return this.writeFunction.apply(exchange, context);
        }
    }


    private static final class BodyInserterResponse<T> extends AbstractServerResponse {

        private final BodyInserter<T, ? super ServerHttpResponse> inserter;


        public BodyInserterResponse(int statusCode, HttpHeaders headers,
                                    MultiValueMap<String, ResponseCookie> cookies,
                                    BodyInserter<T, ? super ServerHttpResponse> body, Map<String, Object> hints) {

            super(statusCode, headers, cookies, hints);
            Assert.notNull(body, "BodyInserter must not be null");
            this.inserter = body;
        }

        @Override
        protected Mono<Void> writeToInternal(ServerWebExchange exchange, Context context) {
            return this.inserter.insert(exchange.getResponse(), new BodyInserter.Context() {
                @Override
                public List<HttpMessageWriter<?>> messageWriters() {
                    return context.messageWriters();
                }

                @Override
                public Optional<ServerHttpRequest> serverRequest() {
                    return Optional.of(exchange.getRequest());
                }

                @Override
                public Map<String, Object> hints() {
                    hints.put(Hints.LOG_PREFIX_HINT, exchange.getLogPrefix());
                    return hints;
                }
            });
        }
    }

}
